Neisserial porins (gonococcal Protein I [PIA or PIB] or meningococcal class 1 [PorA], 2 or 3 [PorB] proteins) are the major protein constituent of the Neisserial outer membrane. They have significant homology in structure and function amongst themselves and other Gram-negative porins. We have previously demonstrated that the Neisserial porins activate B lymphocytes, increasing the surface expression of the costimulatory ligand B7- 2, which improves the B cell's ability to "costimulate" T lymphocytes. The induction of B7-2 expression is directly related to the porins' adjuvant ability. As Neisserial porins are molecules that maintain a common "pattern" present on Gram- negative organisms, it is probable that the activation of antigen presenting cells (APC), including B cells and dendritic cells, is through pattern recognition receptors. A family of these receptors has recently been described by which a number of conserved bacterial products including LPS, bacterial lipopeptides, peptidoglycan, etc., can mediate cell activation and induction of costimulatory molecules. These have been termed Toll-like receptors (TLR) because of their significant homology to receptors present in Drosophila that are important for innate immunity. The TLR family of receptors have also been shown to be the main mediators of innate immune responses that have previously been described for these microbial products. We have preliminary data demonstrating that B cell activation by Neisserial porins is mediated through signaling by one of these TLRs, namely TLR2. The overriding hypothesis of this proposal is that the immune stimulatory effect of Neisserial porins and, therefore, their adjuvant activity, is due to an interaction of the porins with TLR2 on antigen presenting cells (especially B cells and dendritic cells) and this event initiates a set of common signal transduction events that induces cell activation and increases B7-2 and class II MHC surface expression. The following aims of the proposal will attempt to prove this hypothesis: 1) investigate the interaction of Neisserial porin with TLR2 and demonstrate the importance of TLR2 mediated signaling in their adjuvant activity, 2) explore the significance of signal transduction events induced in B cells and dendritic cells (including NF-kappaB activation protein tyrosine kinase activation and MAPKK activation) by Neisserial porins in relationship to their adjuvant activity and whether these events are due to immune cell stimulation through TLR2, and 3) determine whether dendritic cell activation by the Neisserial porins is mediated through TLR2 and if their ability to activate dendritic cells is related to the their immunopotentiating activity.